Cutting tool inserts employed for machining of metals and metallic (i.e., metal-containing) alloys are commonly fabricated from composite materials. Composite materials provide an attractive combination of mechanical properties, such as strength, toughness, and wear resistance, compared to certain other tool materials, such as tool steels and ceramics. Conventional cutting tool inserts made from a composite material, such as cemented carbide, are based on a “monolithic” construction, which means that they are fabricated from a single grade of cemented carbide. As such, conventional monolithic cutting tools have substantially the same mechanical and chemical properties at all locations throughout the tool.
Cemented carbide materials or, more simply, “carbide materials” or “carbides”, comprise at least two phases: at least one hard particulate ceramic component; and a softer matrix of metallic binder. The hard ceramic component may be, for example, carbides of any carbide-forming element, such as, for example, titanium, chromium, vanadium, zirconium, hafnium, molybdenum, tantalum, tungsten, and niobium. A common, non-limiting example is tungsten carbide. The binder may be a metal or metallic alloy, typically cobalt, nickel, iron, or alloys of any of these metals. The binder “cements” the ceramic component within a continuous matrix interconnected in three dimensions. As is known in the art, cemented carbides may be fabricated by consolidating a powder including at least one powdered ceramic component and at least one powdered metallic binder material.
The physical and chemical properties of cemented carbides depend in part on the individual components of the metallurgical powders used to produce the materials. The properties of a particular cemented carbide are determined by, for example, the chemical composition of the ceramic component, the particle size of the ceramic component, the chemical composition of the binder, and the weight or volume ratio of binder to ceramic component. By varying the ingredients of the metallurgical powder, cutting tools, such as cutting tool inserts, including indexable inserts, drills and end mills can be produced with unique properties matched to specific cutting applications.
In applications involving the machining of modern metallic materials, enriched grades of carbide are often utilized to achieve the desired quality and productivity requirements. However, cutting tool inserts having a monolithic carbide construction composed of higher grades of cemented carbides are expensive to fabricate, primarily due to high material costs. In addition, it is difficult to optimize the composition of conventional monolithic indexable cutting inserts composed of single grades of carbide material to meet the differing demands placed on the various regions of the inserts.
Composite rotary tools made of two or more different carbide materials or grades are described in U.S. Pat. No. 6,511,265. At this time, composite carbide cutting tool inserts are more difficult to manufacture than rotary cutting tools. For example, cutting inserts are, typically, much smaller than rotary cutting tools. Also, the geometries, in particular, cutting edges and chip breaker configurations, of current cutting tool inserts are complex in nature. With cutting tool inserts, the final product is produced by a pressing and sintering process, and the process also may include subsequent grinding operations.
U.S. Pat. No. 4,389,952, which issued in 1983, describes an innovative method of making composite cemented carbide tools by first manufacturing a slurry containing a mixture of carbide powder and a liquid vehicle, and then painting or spraying a surface layer of the mixture onto a green compact of a different carbide. A composite carbide tool made in this way has distinct mechanical properties differing between the core region and the surface layer. The described applications of this method include fabricating rock drilling tools, mining tools and indexable cutting tool inserts for metal machining. However, the slurry-based method described in the '952 patent can only be applied to making indexable cutting inserts without chip breaker geometries or, at best, with very simple chip breaker geometries. This is because a thick layer of slurry will alter the insert's chip breaker geometry. Widely used indexable cutting inserts, in particular, must have intricate chip breaker geometries in order to meet the ever-increasing demands for machining a variety of work materials. In addition, performing the slurry-based method of producing composite tools and inserts requires a substantially greater investment in specialized manufacturing operations and production equipment.
Ruthenium (Ru) is a member of the platinum group and is a hard, lustrous, white metal that has a melting point of approximately 2,500° C. Ruthenium does not tarnish at room temperatures, and may be used as an effective hardener, creating alloys that are extremely wear resistant. It has been found that including ruthenium in a cobalt binder in cemented carbide used in cutting tools or cutting tool inserts improves resistance to thermal cracking and significantly reduces crack propagation along the edges and into the body of the cutting tool or cutting tool insert. Typical commercially available cutting tools and cutting tool inserts may include a cemented carbide substrate having a binder phase including approximately 3% to 30% ruthenium. A significant disadvantage of adding ruthenium, however, is that it is a relatively expensive alloying ingredient.
A cutting tool insert including a cemented carbide substrate may comprise one or more coating layers on the substrate surface to enhance cutting performance. Methods for coating cemented carbide cutting tools include chemical vapor deposition (CVD), physical vapor deposition (PVD) and diamond coating.
There is a need to develop improved efficient, low cost cutting tool inserts for metal and metallic alloy machining applications.